| The rheological properties of starch can affect the processing and transportation of starch products,the gel properties of starch are closely related to the quality and stability of starch products,both of them are important for starch application.Insufficient gelatinization refers to changing the starch gelatinization conditions(reducing pH and temperature,etc.)to make starch granules expand in a limited way without losing their identifiable particle morphology.Some properties of insufficient gelatinized starch are better than that of raw starch,however,the effects of this treatment on the two properties of starch are still not clear.Therefore,in this topic eight common potato starch(potato,cassava,sweet potato),legume starch(mung bean,pea),cereal starch(buckwheat,wheat,corn)were selected as the research objects,and the insufficient gelatinization treatments of 160 r/min,50?,5 min of raw starch were carried out,to explore the effects of insufficient gelatinization on the rheological properties and gel properties of starch.The viscosity properties of starches paste were studied by rotational rheometer.Results showed that the peak viscosity of potato starches were the highest(3829-27818 cP)in all three concentrations(5%?10%?15%).At 5% concentration,the final viscosity of starch were reduced(8.2%-47.7%)after insufficient gelatinization treatment,and the decrease(32.4%-47.7%)on potato starch was most obvious.However,the final viscosity of starch were increased(2.5-29.0%)after the treatment at 10% concentration.At 15% concentration,the final viscosity of potato,cassawa,mung beans,pea,wheat,corn starches were increased(1.8%-14.7%,)but sweep potato and straw starches were reduced(3.4%-8.9%)after insufficient gelatinized.The dynamic rheological of starches paste by rotational rheometer showed that,for all starches,the elastic modulus(4.9-2608 Pa at 95?)were greater than the viscous modulus(4.2-215 Pa).The elastic-viscous modulus of cassava starch was the smallest(namely 4.9-43.9 Pa and 4.2-26.3 Pa at 95?)in all concentrations.The elastic-viscous modulus of potato and legume starches varies slightly(8.4%-35.3%)with temperature and their thermal stability are better,while cereal starch varies greatly(42.6%-71.4%)and their thermal stability is poor.At 5% concentration,the modulus of starch was increased(1.4%-43.9%)after insufficient gelatinization(at 95?).At the concentration of 10%,insufficient gelatinization increased(0.7%-80.9%)at 95? on the modulus of starches,only wheat starch was reduced(43.0%-50.1%).At the concentration of 15%,the modulus of starches were increased(0.2%-37.0%)at 95? after insufficient gelatinization,while the modulus of other starches get decreased(2.3%-12.3%).The results of static rheological test by rotational rheometer showed that the fluidity index of mung bean starch was the smallest(0.21-0.80),and that of potato starch was the largest(0.30-0.89).At concentration of 5%,the hysteresis ring area of potato starch was the largest(1296.80 Pa·S?1413.60 Pa·S),the thixotropy is the largest and shear stability is the worst.That of pea starch was the smallest(287.19 Pa·S?299.26 Pa·S).When the starch concentration were 10% and 15%,the hysteresis ring area of mung bean starch was the largest(2488.96-9628.77 Pa·S)and that of corn starch was the smallest(1368.96-7992.80 Pa·S),insufficient gelatinization reduces hysteresis ring area of starch gels(3%-38%),only legume starch enhances(1.9%-50.3%).The texture characteristics of starch gels were determined by physical analyzer.Results showed that the hardness and adhesiveness of legume starch are higher(namely 85.7-782.1 g,52.1-698.0 g),that of cereals starch is smaller(namely 62.1-407.0 g,27.2-367.0 g).At 5% concentration,after insufficient gelatinization,the hardness of starch gels increased by 4.5%-37.2% and the viscosity of starch gels increased(23.3%-98.2%),while it was contrary at the concentration of 10% and 15%,their reduced by 0.3%-17.9% and 0.8%-44.1% respectively.The elasticity and cohesion are relatively small(namely 0.65-1.06 and 0.36-0.97),insufficient gelatinized influenced little on the elasticity and cohesion of starch gels.Discovery that legume starch gel had a good freeze-thaw stability,followed by potato starch gel,and poor starch grains by calculating the rate of water evolution.Insufficient gelatinized enhanced the freeze-thaw stability of starch gel.The microstructure of the starch gel was observed by scanning electron microscopy.It was noticed that each starch gels showed three dimensional reticular structure and the mesh size varies in a wide range(15-420 ?m),but the mesh distribution is uneven,and small amount of debris appears in the gels.Compared to the original starch gel,the starch gels formed after insufficient gelatinization had a better network structure which showed clear mesh,compact connection between holes and the scope is smaller(10-390 ?m),indicating that insufficient gelatinization was favorable for the formation of starch gel.Overall,the network structure of legume starch gel is better,followed by the potato starch gel,and the network structure of cereal starch gel is worst.According to the experimental results,the effect of insufficient gelatinization treatment of 160 r/min,50? and 5 min on starch viscosity,rheological properties and gel properties decreased with increasing concentration,therefore,this method is more suitable for processing starch with 5% concentration.It can increase the viscosity of starch paste,weaken retrogradation,enhance resilience and resistance to mobility,increase thixotropy and weaken shear stability.Enhancing the freeze thaw stability of starch gel and the ability of starch to form gel,the network structure was clearer,the cavity became smaller and the mesh distribution was more uniform. |
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